The present invention relates to techniques for a display device and electronic equipment. In particular, the present invention relates to a liquid crystal display device (abbreviated as LCD) which controls liquid crystal molecules by a horizontal electric field system and the like.
In liquid crystal display devices mounted on various types of electronic equipment, there are an IPS (In-Plane-Switching) system (also referred to as mode), an FFS (Fringe Field Switching) system and the like as the horizontal electric field system. The horizontal electric field system is advantageous in such points as a wide viewing angle and an aperture ratio (area ratio of a region effective for display in one pixel region) as compared with a vertical electric field system.
As an example of a prior art technique relating to the FFS, there is Japanese Patent Application Laid-Open Publication No. 2008-52161 (Patent Document 1). The Patent Document 1 (Liquid Crystal Device and Electronic Equipment) describes a liquid crystal device of an FFS system which realizes a bright display with a high aperture ratio without making a configuration of the device complicated.
In the IPS mode, a pixel electrode and a common electrode are provided in the same layer, and electric field is mainly generated in a direction parallel to a substrate surface (defined as X and Y directions). Therefore, electric field is hardly formed in a region just above the pixel electrode, so that it is difficult to drive liquid crystal molecules in the region positioned just above the pixel electrode.
On the other hand, in the FFS mode, a pixel electrode and a common electrode are provided so as to be stacked in a direction perpendicular to a substrate surface (defined as Z direction) via a dielectric film interposed therebetween, and electric field in an oblique direction with respect to the substrate surface or in a parabolic shape (also referred to as fringe electric field) is generated. Therefore, even the liquid crystal molecules in a region positioned just above the pixel electrode can be easily driven. More specifically, an aperture ratio higher than that in the IPS mode can be obtained in the FFS mode. Hereinafter, an electrode positioned on an upper side in the stacked electrodes is referred to as an upper electrode (first electrode), and an electrode on a lower side is referred to as a lower electrode (second electrode).